1. Field of the Invention
The present invention relates generally to ATM-LAN networks where LAN emulation clients access to a LAN emulation server, and more specifically to a bridge for establishing communication among LAN segments or between any one of the LAN segments and an ATM network.
2. Description of the Related Art
In a known ATM-LAN network as disclosed in Japanese Laid-Open Patent Specification Hei-8-56227, each one of interconnected ATM nodes serves both ATM terminals and LAN terminals and includes a cell switching unit, a LAN emulation unit and a packet transfer unit. The LAN emulation unit has a bridging function at the level of medium access control (MAC) sublayer and the packet transfer unit has a routing function at the level of network layer. These units are connected to a transmission line via the cell switching unit. Communication between LAN terminals on different LAN segments involves the use of a LAN interface which segments a MAC frame from the source terminal into 53-byte cells and forwards them through a cell switching unit to the LAN emulation unit, where it reassembles the cells into a MAC frame for routing (bridging) at the MAC-sublayer level, appends a VCI (virtual channel identifier) to the frame, segments it again into cells and then forwards them through the cell switching unit to the destination. Therefore, a substantial amount of time is involved to process the LAN emulation protocol for bridging different LAN segments of an ATM-LAN network.
It is therefore an object of the present invention to provide an ATM-LAN network where bridged communication between LAN segments is established in a short period of time.
According to a broader aspect, the present invention provides a communication network comprising an ATM network, a plurality of LAN segments each serving a plurality of LAN emulation clients, and a bridge having a memory for storing addresses of the LAN emulation clients. The bridge receives a frame, examines its address with contents of the memory, and establishes communication between the LAN segments without using LAN emulation protocol if the frame is determined to be destined for a LAN segment connected to the bridge or establishes communication between the LAN segments via the ATM network using the LAN emulation protocol if the frame is determined to be destined for a LAN segment which is not connected to the bridge.
According to a second aspect of the present invention, there is provided a communication network comprising an ATM network, a LAN emulation server connected to the ATM network, a plurality of LAN segments each having at least one LAN emulation client, and a bridge comprising a plurality of ports uniquely identified by port numbers and connected to the LAN segments and the ATM network, a memory having a plurality of entries, a plurality of buffer means for receiving a frame from the ports, the frame containing source and destination data-link-layer addresses, and means for storing into the memory the source data-link-layer address of the frame and the port number of a first port of the plurality of ports from which the frame was received, making a search through the memory for an entry containing the destination address of the frame, forwarding the frame onto a second port of the plurality of ports identified by a port number contained in the entry if the entry is found in the memory, the second port being different from the first port, transmitting an address resolution request to the LAN emulation server via the ATM network to obtain a destination ATM address corresponding to the destination data-link-layer address if the entry is not found in the memory, transmitting a connection setup request to the ATM network to establish a virtual connection in the ATM network according to the destination ATM address, and forwarding the frame onto the port to which the ATM network is connected.